Single factors of authentication by themselves can have security issues. For example, if a hacker acquires a user's password, then the hacker may be able to gain access to other network resources for which the user has registered the same password for authentication. Therefore, to increase security, many enterprise applications, cloud applications, mobile applications, and other networked resources require more than one factor of authentication. For example, in addition to a username and password, a network resource may require the user to authenticate with a second factor of authentication, such as a one-time password, a digital signature based on a certificate, etc.
When two or more factors of authentication are required, a hacker has more difficulty acquiring all of the information necessary to access a user's network resources. However, multi-factor authentication is typically more burdensome for users.